Evolutional features and influencing factors of Carboniferous-Permian hydrocarbon source rocks in Ejin Banner and its vicinities, western Inner Mongolia.

Based on the characteristics of planar and longitudinal distribution of the evolution degrees of Carboniferous-Permian hydrocarbon source rocks in Ejin Banner and its vicinities, together with the study of the outcrop distribution of intrusive rocks of middle-late Hercynian to Himalayan period and their activity characteristics, the authors hold that the evolution degree of Carboniferous-Permian hydrocarbon source rocks was mainly controlled by intrusive rocks and tectonic activity of late Hercynian and Yanshanian period. The intrusive rocks and tectonic activity of Indo-Chinese period only affected the evolution degree in several sections, and the intrusive rocks and tectonic activity of Himalayan period failed to affect the evolution degree. Over-mature hydrocarbon source rocks of Carboniferous-Permian Amushan Formation (Ganquan Formation) and Lower-Middle Permian Jushitan Formation were mainly affected by intrusive rocks and tectonic activities of late Hercynian period, and the intrusive rocks and tectonic activities of Yanshanian period affected Upper Permian Haersuhai Formation. On such a basis, the effects of different stages of intrusive rocks and tectonic activities on the plane distribution of evolution degrees of Carboniferous-Permian hydrocarbon source rocks are determined. It is considered that there existed no regional metamorphism of Carboniferous-Permian hydrocarbon source rocks, the general maturity was mature-highly mature, the evolution degree of several sections was higher (over-mature), caused by thermal metamorphism of intrusive rocks and dynamic metamorphism of tectonic activitiesy. The evolution degree of Carboniferous-Permian hydrocarbon source rocks in the region of weak magmatism and tectonic activities after Carboniferous-Permian was moderate (mature-highly mature).